The nano technique is one of the most popular research fields today. It brings a new industrial revolution and a great strike to the economy and social development. Subsidy from official institute for Nano-technique research also makes a multiple growth of industry in many countries. As stated by Professor Kari Rissanen of Jyvaskyla University, using Nano techniques would make the scale of systems or facilities apparently minimized and the other characteristics can be remained still. Nano electrons are able to be speeded up and make the computer more efficient. New techniques which can be used to store information inside the molecule may increase the storage capacity of electronic facilities. Therefore, it is obviously that Nano-chemistry, Nano-biology and Nano-physics would open a new stage for those domains such as medicine science, energy environment and optics.
Between 1997 and 1999, TEKES and Academy of Finland have supported 16 projects of Nano-technology research. Among them, the project of CHANIL of VTT had been run for 2 years, and the main purpose of the project was to develop the Nano Imprint Lithography (NIL) technology, which is able to create a sub-100 nm pattern with low cost.
NIL is a compression molding technique invented by Stephen Chou at University of Minnesota in 1996. A mold is heated and pressed into a thin polymeric (ex. PMMA—Polymethyl Methacrylate) film that have been coated on the wanted substrate. After the cooling and the separation between mold and polymeric layer, the stereo patterns will be completely transferred. After the treatment of dry etching such as plasma etching or RIE (Reactive dry etching), the residual layer will be removed and the wanted patterns will be achieved.
Recently, Princeton University proposed a method that produces Metal Oxide Semiconductor Field-Effect Transistor (MOSFET) element by using the way of Nano imprint lithography technique on a 4-inch wafer.
On the other hand, Prof. Wilson (University of Texas, Austin) uses UV-curing polymer as transfer layer in developing the NIL technique, called the “Step and flash” technique which makes the pattern transfer at low temperature possible. The overall process is shown as FIG. 12. The etching barrier shown as in FIG. 12 is a coated layer which is formulated by cross-linkable monomers, said the photoresist.
As the conventional imprint technique, Step and Flash technique needs to use plasma or other dry etching process to remove the residual layer till the substrate exposed to atmosphere. By this way, both the wanted pattern and the residual layer will be etched and it will make the resist patterns thinner. While taking the cost into consideration, conventional optical lithography cost less. But we all know that resist which is supposed to be removed will be washed by developer from the surface to the substrate (as shown in FIG. 13). So the period of developing must be controlled precisely or the developer would damage the reserved patterns. As shown in FIG. 14 & 15, in the process of a conventional optical lithography, we need the parallel light to produce a straight side wall of the photoresist to avoid the scattering and reflection effect that would make additional unwanted photosensitive reaction.
Furthermore, while transferring the high aspect ratio patterns, we usually need thick resist layer, as shown in FIG. 16 and subsequent limitation in resolution will be caused by the longer distance that light has the more deviation.
Nevertheless, both dry etching machine for nanoimprint lithography and high performance exposure equipments for optical lithography cost lot. Therefore, we need a new method to make this work faster, cheaper and more efficient and combining the imprint and optical lithography will be the solution.